One of the major systems in the human body is the circulatory system. Components of the circulatory system include the heart, blood vessels, and blood, all of which are vital for the transportation of materials between the external environment and the cells and tissues of the body.
The blood vessels are the network of passageways through which blood travels in a human or animal body. Specifically, the arteries carry oxygenated blood away from the left ventricle of the heart. The arteries are arranged in progressively decreasing diameter and pressure capability from the aorta, which carries the blood immediately out of the heart to other major arteries, to smaller arteries, to arterioles, and finally to capillaries, where exchange of nutrients and waste products between the blood and the cells and tissues of the body occur. Generally, veins carry oxygen depleted blood back to the right atrium of the heart using a progressively increasing diameter network of venules and veins.
Angiography is a procedure used in the diagnosis and treatment of cardiovascular conditions including abnormalities or restrictions in blood vessels. During angiography, a radiographic image of the heart or a vascular structure is obtained by injecting a radiographic contrast material through a catheter into a vein or artery. The injected contrast material can pass to vascular structures in fluid communication with the vein or artery in which the injection is made. X-rays are passed through the region of the body in which the contrast material was injected. The X-rays are absorbed by the contrast material, causing a radiographic outline or image of the blood vessel containing the contrast material. The x-ray images of the blood vessels filled with contrast material are usually recorded onto film or videotape and are displayed on a fluoroscope monitor.
Angiography provides an image of the cardiac or vascular structures in question. This image may be used solely for diagnostic purposes, or the image may be used during a procedure such as angioplasty where a balloon is inserted into the vascular system and inflated to open a stenosis caused by atherosclerotic plaque buildup.
Currently, during angiography, after a catheter is placed into a vein or artery (by direct insertion into the vessel or through a skin puncture site), the angiographic catheter is connected to either a manual or an automatic contrast injection mechanism.
A simple manual contrast injection system typically has a syringe and a catheter connection. The syringe includes a chamber with a plunger therein. Radiographic contrast material is suctioned into the chamber. Any air is removed by actuating the plunger while the catheter connection is facing upward so that any air, which floats on the radiographic contrast material, is ejected from the chamber. The catheter connection is then attached to a catheter that is positioned in a vein or artery in the patient.
The plunger is manually actuated to eject the radiographic contrast material from the chamber, through the catheter, and into a vein or artery. The user of the manual contrast injection system may adjust the rate and volume of injection by altering the manual actuation force applied to the plunger.
Often, more than one type of fluid injection is desired, such as a saline flush followed by the radiographic contrast material. One of the most common manual injection mechanisms used today includes a valve mechanism which controls which of the fluids will flow into the valuing mechanism and out to the catheter within the patient. The valve mechanism can contain a plurality of manual valves that the user manually opens and closes to direct fluid flow to a particular fluid channel. When the user aspirates or injects contrast fluid into or out of the chamber, the fluid flows through the path of least resistance directed by the position of the valves. By changing the valve positions, one or more other fluids may be injected.
Manual injection systems are typically hand actuated. This allows user control over the quantity and pressure of the injection. However, generally, most manual systems can only inject the radiographic contrast material at maximum pressure that can be applied by the human hand (i.e., 150 p.s.i.). Also, the quantity of radiographic contrast material is typically limited to a maximum of about 12 cc. Moreover, there are no safety limits on these manual contrast injection systems which restrict or stop injections that are outside of predetermined parameters (such as rate or pressure) and there are no active sensors to detect air bubbles or other hazards.
Currently used motorized injection devices consist of a syringe connected to a linear actuator. The linear actuator is connected to a motor, which is controlled electronically. The operator enters into the electronic control a fixed volume of contrast material to be injected at a fixed rate of injection. Typically, the fixed rate of injection consists of a specified initial rate of flow increase and a final rate of injection until the entire volume of contrast material is injected. There is no interactive control between the operator and machine, except to start or stop the injection. Any change in flow rate must occur by stopping the machine and resetting the parameters.
The lack of ability to vary the rate of injection during injection can result in suboptimal quality of angiographic studies. This is because the optimal flow rate of injections can vary considerably between patients. In the cardiovascular system, the rate and volume of contrast injection is dependent on the volume and flow rate within the chamber or blood vessel being injected. In many or most cases, these parameters are not known precisely. Moreover, the optimal rate of injection can change rapidly, as the patient's condition changes in response to drugs, illness, or normal physiology. Consequently, the initial injection of contrast material may be insufficient in volume or flow rate to outline a desired structure on an x-ray image, necessitating another injection. Conversely, an excessive flow rate might injure the chamber or blood vessel being injected, cause the catheter to be displaced (from the jet of contrast material exiting the catheter tip), or lead to toxic effects from contrast overdose (such as abnormal heart rhythm).
At present, the operator can choose between two systems for injecting contrast material: a manual injection system which allows for a variable, operator interactive flow rate of limited flow rate and a preprogrammed motorized system without operator interactive feedback (other than the operator can start/stop the procedure). Accordingly, there is a need for improvement in the equipment and procedures used for performing diagnostic imaging studies.